1. Field of the Invention
The present invention relates to an apparatus for spraying an air-water mist to be used for cooling a cast strand in continuous metal casting.
2. Description of the Prior Art
A water spraying method has been conventionally and generally used as cooling means for a cast strand which is continuously pulled out in a continuous metal casting process; however, recently a air-water mist cooling method has become the main method whereby the surface cracks of a cast strand are reduced wherein the quantity of the water to be consumed is small and the cooling efficiency is high.
In general, a cylindrical nozzle whose both ends are closed is used as a mist spraying apparatus and a slit-like exhaust hole which is parallel to the direction of diameter is formed and opens in the spraying side wall on the peripheral surface of the mist atomizing nozzle. On the other hand, a air-water mixture supply pipe communicates with the introduction side wall on the side opposite to the spraying side wall. In this construction, the central axis of the introduction inlet of the edge portion of the air-water mixture supply pipe and the central line passing through the midpoint of the exhaust hole of the mist atomizing nozzle which is parallel to that central axis are arranged substantially in line.
Due to this, relatively large water droplets in the air-water mixture supply pipe are sprayed from the exhaust hole without being formed as the mist. Consequently, it has been impossible to make the most of the advantages as a feature of the mist cooling method, such as improvement in surface cracks of a cast strand or in cooling efficiency utilizing the latent heat of vaporization of the mist.
In addition, another method is known whereby an orifice is provided at the introduction inlet of the edge portion of the air-water mixture supply pipe in order to make water droplets fine (i.e. Japanese Patent Kokai (Laid-Open) No. 12347/82). However, it is troublesome to form an orifice, the cost of the whole spraying apparatus is increased and a problem occurs in that if the orifice is choked with a foreign matter, it is extremely difficult to remove. There is, furthermore, a fear that unless the pressures of the air and water on the supplying side are raised, the cooling ability may be lacking since the quantity of the mist to be sprayed from the exhaust hole will be insufficient.